In the highly competitive disk drive industry, there is a continuing effort to reduce cost including the manufacturing cost, but not at the expense of reliability and quality. A vital element of the testing to assure quality, performance and reliability is the disk surface analysis to assure the flatness necessary to permit transducer heads to fly over the surface at a height of 1.8 microinches as well as evaluating the magnetic integrity of the data storage tracks.
Surface analysis testers, like the harmonic ratio flyheight (HRF) test, have been a common test procedure. The HRF glide testing is used to detect the presence or absence of mechanically protruding surface defects that interfere with the head/slider. The HRF test is effective, but requires expensive external testers that are typically placed in the manufacturing clean rooms. The HRF process samples every Nth track, called here subsampling, and determines the presence or absence of protruding defects. The subsampling used for HRF is typically every 30th to 40th track with the subsampling period less than the minimum rail width on a slider. The HRF test is an expensive low bandwidth instrumentation system that requires separate manual handling of each disk drive. Due to the smaller air bearings of future sliders and increased rotational velocity, rail contact time with a protruding defect is much shorter and the signal suggesting a defect is much shorter. This means that the HRF system needs a much higher bandwidth for reliable detection, which will make the HRF system even more expensive. Further, the thermal response of the current state of the art magnetoresistive (MR) heads can not be used since future very high speed disk drive recording bandpass channels are AC coupled with lower edge frequency set to about 5 MHz which effectively blocks the thermal response. Accordingly, a surface analysis test method is sought that will replace the HRF based method without sacrificing the reliability and quality of the disk drives being produced while lowering cost.